The present invention relates to a device of refractory porous material for blowing gas under pressure into a bath of liquid metal.
It is known for quite some time to manufacture from refractory material of a certain grain size (French Pat. No. 1,094,809) elements of the type which are incorporated into the refractory walls of a metallurgical receptacle containing a bath of molten material in order to blow into the bath of molten material a mixing gas and to interrupt this blowing, whenever desired, without the risk of penetration of the molten metal into the device as is the case with tuyeres.
In such devices it is, as known, absolutely necessary to prevent flow of gas into the liquid metal at the interface of the device and the refractory wall of the receptacle in which the bath of molten metal is maintained.
For this purpose it is also known to closely surround the refractory element by a metallic envelope, made for example of a sheet of steel, which is closed at one of its ends by a base plate provided with means for feeding the gas under pressure therethrough. The envelope and the base plate thus define a receptacle in which the porous mass is exposed only on one of the free faces which is destined to contact the liquid metal.
The use of such an envelope has, in addition to its function of providing lateral tightness, further advantages among which can be mentioned the possibility to constitute in connection with the base plate a casting mold for the porous mass and, on the other hand, due to its regular and smooth outer surface to permit its tight application to an opening formed in the wall of refractory material which is to receive the element, or to facilitate withdrawal of the element for its displacement after the wear of the same (French Pat. of addition No. 65,904). The envelope also serves as an armature to protect the mass of porous material against eventual shocks applied thereto during transport or handling of the element.
Besides its many advantages, the presence of a metallic envelope leads quite often to a number of disadvantages which result quite often in a rapid deterioration of the original fluid tightness at the interface of the porous mass and the envelope in such a manner that the latter is not any longer capable of carrying out the function for which it was provided.
The inventors have established from their experience that, after repeated blowing of gas through this known device provided with an outer metallic envelope, the latter suffers from permanent deformation in such a way that when no gas is blown through the device, the liquid metal will penetrate into the thus-formed space between the envelope and the porous mass.
Such metal infiltration will render the device prematurely unusable, since, on the one hand, there will form closely adjacent thereto privileged passages for the gas; the major portion thereof will thus not pass through the porous mass, and, on the other hand, the metal may penetrate deeply into the element until it blocks the means for feeding the gas incorporated into the base of the element, which of course is not without certain dangers.